Simulation of Electricity Production by a Solar Tower Power Plant with Thermal Storage System in Algeria

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Simulation of Electricity Production by a Solar Tower Power Plant

with Thermal Storage System in Algeria

IKHLEF Khaoula^#1, LARBI Salah^#2

#Ecole Nationale Polytechnique d’Alger (ENP), Laboratoire de Génie Mécanique et Développement (LGMD) 10, Avenue Hassen Badi, BP182, El Harrach, Alger, Algérie

1[email protected]

2[email protected]

Abstract— Concentrating solar tower power plant with thermal storage system has received particular attention among researchers, power- producing companies and policymakers according to its bulk electricity generation ability by overcoming the intermittency of solar energy. The parabolic trough collector and solar tower are the two dominant CSP systems which are either operational or in the construction stage.

The aim of this paper is to study the production of electricity by a solar tower power plant with thermal storage system (type PS10). The power plant capacity is 150MWe and it is located in Hassi R'mel (south region of Algeria). The purpose is to highlight the importance of developing concentrating solar thermal technologies in Algeria.

Concentrating solar thermal technologies belong to an engineering field, which can significantly contribute to the delivery of clean, stainable energy worldwide.

Keywords

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Solar Tower Power Plant, Thermal Storage System, Simulation, System Advisor Model.

Abbreviations

CCGT Combined Cycle Gas Turbine CDSEP Crescent Dunes Solar Energy Project CF Capacity Factor

CRS Central Receiver Systems CSP Concentrating Solar Power DNI Direct Normal Irradiation DSG Direct Steam Generation HTF Heat Transfer Fluid

ISEGS Ivanpah Solar Electric Generating System LFR Linear Fresnel reflector

PD Parabolic Dish

PTC Parabolic Trough Collector SAM System Advisor Model SM Solar Multiple SPT Solar Power Tower

I. INTRODUCTION

In order to take up the global challenges of clean energy, climate change and sustainable development, it is necessary to boost the development of environmentally friendly energy technologies. In this context, concentrating solar power plants (CSP) are increasingly relevant because of the need to reduce carbon dioxide emissions in electricity production and heat generation required to reach the goal of

limiting climate change to 2°C above the pre-industrial levels.

CSP power plants are gaining in popularity with advances in technology. There is a type of concentrating solar thermal technologies available nowadays, being solar thermal collectors the major component of solar power systems. As previously stated, these collectors receive the incoming radiation and concentrate solar rays to heat a fluid, which then directly or indirectly drives a turbine and converted mechanical energy into electricity through a generator. The concentration of sunlight allows the fluid to reach working temperatures high enough to ensure affordable efficiency in turning the heat into electricity, while limiting heat losses in the receiver. The four main commercial CSP technologies are distinguished by the way they focus the sun’s rays and the technology used to receive the solar energy (Fig. 1): parabolic trough collector (PTC), solar power tower (SPT), linear Fresnel reflector (LFR) and parabolic dish (PD). The basic principles of concentrated CSP systems are covered in previous reference works such as [1], [2], [3], [4] and [5].

Fig. 1 Categories of CSP technologies.

International Journal of Control, Energy and Electrical Engineering (CEEE) Vol.8 pp.7-10

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In the SPT plants (see Fig. 2), also called central receiver systems (CRS) or power tower, a large number of computer- assisted mirrors (heliostats) track the sun individually over two axes. Heliostats are less expensive than trough mirrors because they used standard flare glass, instead of glass that is manufactured at specific curves. They concentrate the solar radiation onto a single receiver at the top of a central tower where the solar heat drives a thermodynamic cycle and generates electricity. SPT plants can achieve higher temperatures than PTC and LFR systems because they have higher concentration factors. The SPT can use water-steam (DSG), synthetic oil or molten salt as the primary heat transfer fluid [6].

Fig. 2 Schematic of a Solar Tower Power Plant.

The number of existing CSP SPT plants of significant size is very limited, and the time they have been operational is also minimal. Additionally, not all the data needed are publicly available. Hence, the full potential of the SPT technology is not shown by the surveys of plants. In the list of the SPT plants of [7], there are only 34 CSP SPT plants worldwide. Only

3 above 20 MW of capacity are operational, ISEGS of 377 MW capacity since 2014, Crescent Dunes Solar Energy Project (Tonopah) of 110 MW capacity since 2015, and Khi Solar One of

50MW capacity since 2016. The 377 MW ISEGS plant only producing 703,039 MWh/year

(2016), the output of a medium to small scale CCGT plant, has the best data set covering 3 years.

Recently, there has been a particular interest to solar tower power technology, as is evident from the fact that there are several companies involved in planning, designing and building utility size power plants. This is an important step towards the ultimate goal of developing commercially viable plants. There are numerous examples of case studies of applying innovative solutions to solar power [8].

II. RESULTS AND DISCUSSIONS

The solar power tower simulation is performed using the System Advisor Model (SAM) simulator. The meteorological data of the selected site are taken by METEONORM

7 software with period data (1991-2010) for numerical simulation. Some important design parameters used in the simulation are given by tables, I, II and III.

TABLEI HELIOSTAT FIELD

Total heliostat

reflective area Heliostats number Mirror washing

1269055 m² 8790 0.70L/m²and 63

washes per year TABLEII

POWER CYCLE

Solar multiple Capacity Cycle Condenser type

2 150 MWe Rankine Air-cooled

HTF type HTF temperature HTF mass flow rate Salt (60% NaNO3,

40% KNO₃ )

Hot: 574°C

Cold: 290°C 850.9 kg/s TABLEIII

THERMAL STORAGE

Type Full load

hours Tank volume Hot tank heater capacity

Two tank 6 11087 m³ 30MWe

Figures 3, 4 and 5 illustrate the meteorological data of Hassi R'Mel site.

0 2 4 6 8 10 12

3,0 3,5 4,0 4,5 5,0

Wind velocity

Months

Wind velocity [m/s]

Relative humidity [%]

Ambient temperature[°C]

10 20 30 40 50 60

Temperature - Humidity

Fig. 3 Wind velocity, temperature and humidity.

0 2 4 6 8 10 12

0 200 400 600 800 1000

DNI [ W/m²]

Months

Minimum Average Maximum

Fig. 4 Direct normal irradiation.

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 4

6 8 10 12

Duration [h]

Months Fig. 5 Hours of sunshine.

The hours of sunshine are the hours whose DNI is greater than 300W/m² the threshold of deliverability of the plant.

Figure 6 illustrates the changes in the monthly averages of the production capacity of the power plant. Notice that the production varies proportionally to the DNI. Thus, the decrease in the production capacity from the incident radiation to the net power produced is caused by the optical, thermal and parasitic losses generated in the installation.

0 1 2 3 4 5 6 7 8 9 10 11 12 13

100 150 200 250 300

350 DNI [W/m²] Q incident [MW] Q reflected [MW]

Q useful [MW] E gross [MW] E net [MW]

DNI [W/m²]

Months

0 50 100 150 200 250 300 350 400 450

Energy [MW]

Fig. 6 Average monthly production capacity of the solar power plant.

The net hourly production capacity of the different months is given by figure 7.

0 50 100 150 200

Net production [MW]

Months

1 2 3 4 5 6 7 8 9 10 11 12

Fig. 7 Hourly production capacity of the solar power plant.

According to this figure, the best production is reached in the summer period, which records values that exceed 150 MW, where the plant works in an overcapacity.

Figures 8 and 9 show the monthly average daily production of the plant with a storage system that actually starts from a DNI greater than 300W/m² for the two typical days in May and January.

For the typical day of May, the energy incident, absorbed and reflected by the solar field follow the same shape as the DNI. The other energies (useful, gross and net) follow the variation of the DNI until 18h where they continue to be generated despite the disappearance of the DNI (null DNI).

This generation of energy is provided by the storage tanks.

0 2 4 6 8 10 12 14 16 18 20 22 24 0

100 200 300 400 500 600 700

800 May month

DNI [W/m²]

Hours

DNI [W/m²] Q incident [MW] Q reflected [MW]

Q useful [MW] E gross [MW] E net [MWe]

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Energy [MW]

Fig. 8 Monthly average daily production of the power plant (21May).

0 2 4 6 8 10 12 14 16 18 20 22 24 0

100 200 300 400 500

600 January month

DNI [W/m²]

Hours

DNI [W/m²] Q incident [MW] Q reflected [MW]

Q useful [MW] E gross [MW] E net [MWe]

0 100 200 300 400 500 600 700

Energy [MW]

Fig. 9Monthly average daily production of the power plant (21January).

For the typical day of January, all energies follow the same shape as the DNI. The production of electricity starts when the DNI exceeds 300W/m². The power plant operates approximately one-third of its capacity.

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A. Validation

To validate the results of our simulations, the Crescent Dunes Solar Energy Project is chosen. The project has a capacity of

125MWe [9] and 1.1 GW-hours of energy storage [10]. The site is located closely to Tonopah at approximately 310km from northwest of Las Vegas [11, 12]. It is the first utility-scale CSP plant with a solar tower and advanced molten salt energy storage technology from Solar Reserve.

Results comparison between theoretical and experimental data are illustrated on table IV.

TABLEIV RESULTSCOMPARISON

CDSEP [13] Our simulation

Capacity 125MWe 150MWe

Storage system 10h 6h

Total collector area 1200000 m² 1269055 m² Site resource 2685 kWh/m²/yr 2828 kWh/m²/yr

CF more than 50% 57,9%

Annual net output 196 GWh (2018) 223,11GWh

III. CONCLUSIONS

The CSP STP plant technology is still far from the standards of conventional power plants in the power industry, where the actual costs and performances are usually close to the planned values. More experience must be gathered to proper develop a technology that appears to be still in its infancy. The different alternatives that are presently under study at different stages of development may only progress slowly, benefiting from real world

experiences requiring time rather than simulations or laboratory experiments. This paper illustrates a simulation of a solar power tower with a capacity of 150MWe with heat storage system and the importance of installing such power plant in Algeria.

The main conclusions are presented as follows:

1) The parameters that have a great influence on the energy produced are the DNI and the duration of sunshine.

2) Thermal energy storage system plays a positive role in annual electricity generation and system capacity factor.

3) The results of this study were compared with those of the CDSEP power plant. Good agreement is observed between theoretical results and experimental data.

To make these technologies competitive with conventional fossil-based technologies, a reduction in the cost of production must be sought in the years to come.

This objective will be achieved on one hand, thanks to the technological innovations brought by the research and development work on solar sectors and their components (mirrors, panels, receivers, fluids and storage) and on the other hand by the massive construction of these power plants around the world.

REFERENCES

[1] Romero-Alvarez, M. and Zarza, E., Concentrating solar thermal power.

Handbook of energy efficiency and renewable energy, 2007:21-1.

[2] Müller-Steinhagen, H. and Trieb, F., Concentrating solar power. A review of the technology. Ingenia Inform QR Acad Eng, 2004, 18:43- 50.

[3] Zhang, H.L., Baeyens, J., Degrève, J. and Cacères, G., Concentrated solar power plants: Review and design methodology. Renewable and Sustainable Energy Reviews, 2013, 22:466-481.

[4] Barlev, D., Vidu, R. and Stroeve, P., Innovation in concentrated solar power. Solar Energy Materials and Solar Cells, 2011, 95(10):2703- 2725.

[5] Winter, C.J., Sizmann, R.L. and Vant-Hull, L.L. eds., 2012. Solar power plants: fundamentals, technology, systems, economics. Springer Science & Business Media.

[6] Mehos, Turchi, Vidal, et al, Concentrating Solar Power Gen3 Demonstration Roadmap, NREL/TP-5500- 67464, January 2017.

[7] National Renewable Energy Laboratory (NREL), Power Tower Projects, www.nrel.gov/csp/solarpaces/power_tower.cfm, Retrieved November 9, 2017.

[8] Joseph Perkins, Solar Power in the News, http://pointfocus.com/.

[9] Grupo COBRA, Crescent Dunes Solar Thermal Power Plant, Retrieved 15 January 2016.

[10] CleanTechnica, Crescent Dunes 24-Hour Solar Tower Is Online, 22 February 2016. Retrieved 15 June 2016.

[11] Loan Programs Office (LPO), Dept. of Energy (DOE), Energy Department Finalizes $737 Million Loan Guarantee to Tonopah Solar Energy for Nevada Project, 28 September 2011. Retrieved 2 July 2014.

[12] Loan Programs Office (LPO), Dept. of Energy (DOE), Crescent Dunes: Project under construction, 1 September 2015. Retrieved 17 January 2016.

[13] Albert Parker, The Failure of Solar Tower Thermal Energy Storage, Published on May 3, 2018.

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